1. Field of the Invention
The present invention relates to an ultrasonic probe and a method of manufacturing an ultrasonic probe, and more particularly to a structure of a layered array transducer for use in ultrasonic diagnosis of a living body and a method of manufacturing the same.
2. Description of Related Art
2D array transducers (including sparse 2D array transducers) and 1.5D array transducers are known as array transducers having a plurality of transducer elements arranged in an array. In these array transducers, because the size of each transducer element forming an array transducer is very small, the electrical impedance of each transducer element is very high and this prohibits electrical impedance match between each transducer element and a cable (or an apparatus body). This causes significant loss of sensitivity.
In order to deal with the above problem, a technique of forming each transducer element into a layered structure has been proposed. According to this technique, each transducer element is made up of a plurality of piezoelectric layers and a plurality of electrode layers which are laminated in a predetermined order to form a layered assembly. More specifically, a bottom electrode layer and a top electrode layer are provided on the bottom and top surfaces of a layered assembly, respectively, and an inner electrode layer is formed between two adjacent piezoelectric layers. The odd numbered electrode layers in these electrode layers function as signal electrode layers, for example, whereas the even numbered electrode layers function as ground electrode layers, for example. A voltage signal is applied between a plurality of signal electrode layers and a plurality of ground electrode layers. With this structure, it is possible to reduce the electrical impedance of the transducer elements.
The layered transducer elements as described above, however, have a problem of electrical connection with regard to a plurality of electrode layers, in particular, a problem of how a lead or the electrode layer is connected to a plurality of inner electrode layers. According to one example method conventionally used, a via (a thin conductive line passing through the center, for example, of the transducer element in the vertical direction) is used for such connection. This method, however, also has a problem that because the area of the transducer element is very small, applying any process to a completed transducer element is difficult in terms of manufacturing and is not practical.
Japanese Patent Laid-Open Publication No. 2001-29346 discloses an array transducer comprising a plurality of layered transducer elements. In the array transducer disclosed in this publication, in order to eliminate or reduce the above-described problem of the conventional art, a ground side electrode layer connected to a ground inner electrode is formed on a first side surface of each layered transducer element whereas a signal side electrode layer connected to a signal inner electrode layer is formed on a second side surface (opposite to the first side surface) of each layered transducer element. When attention is paid to two adjacent transducer elements in such an array transducer, the signal side electrode layer of one transducer element and the ground side electrode layer of the other transducer element are adjacent to each other and are formed in such a manner that they are shifted from each other in the vertical direction. In order to enhance characteristics of the array transducer, it is desired that electrical insulation be further increased. It is also desirable to increase the positioning accuracy and simplify fabrication of an array transducer (such as simultaneous formation of a pair of opposing side electrode layers, for example). Further, it is desirable to appropriately generate an electric field in each transducer element.